Method of making ferrous metal abrasive



Jan. 14, 1941. w SHAW 2,228,287

METHOD OF MAKING FERROUS METAL ABRASIVE Filed Sept 27, 1938 INVENTOR. M/fr'afir fi. 6%axa BY MJ7WM ATTORNEY Patented Jan. 14, 1941 UNITED STATES PATENT OFFICE William H. Shaw, South Bend, Ind., assignor to The American Foundry Equipment Company, Mishawaka, Ind., a corporation of Delaware Application September 27, 1938, Serial No. 231,945

12 Claims.

The present invention relates to the art of making steel or iron abrasive particles, commonly known as shots, for use in blast cleaning. Such metal shot is projected at high velocity by means of an air blast or centrifugal projecting apparatus against the surface of the material to be cleaned or abraded. It is, therefore, a requisite of the metallic abrasive material or shot that its individual particles be not only hard, but strong and tough in order that they will produce a satisfactory abrading action and at the same time will have a relatively long life and durability.

The general object and nature of my invention is to provide a ferrous metal abrasive of improved physical properties and a novel process for producing it wherein such physical properties are controlled as well as the variation in particle size of the abrasive shot.

Heretofore such ferrous metal abrasive shot has been commercially produced by means of a water spray impinging against a stream of molten metal (ferrous metal of relatively high carbon content, such as gray iron), in order to disperse the latter into divided particles, and then catching or retrieving such dispersed particles in a water quenching tank. The product of such a prior process is relatively hard due to the predominance of the cementite constant, but is also quite brittle. Therefore, it has previously been found necessary in order to subject such a product to a subsequent heat treatment, such as heating to a temperature above 1750 F. in order to redissolve the predominant cementitic structure to such a point that the brittleness incident to the presence thereof is substantially reduced.

In my present process, however, I have found that the steps of dispersing the stream of molten metal into divided particles and heat treatment in order to produce a predominance of martensite with a corresponding reduction in the percentage of cementite can be simultaneously obtained. My process also embodies the improvement of enabling an efficient and satisfactory control of the variations in particle size of the resultant prod uct. Briefly outlined, my process comprises the steps of dispersing the stream of molten metal into divided particles, slowly cooling such particles (by means of air cooling) through the upper critical temperature or just below the solidus temperature, and then rapidly cooling or quenching (by means of a water quench) to atmospheric temperature.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means hereinafter fully described and particularly pointed out in the claims.

The annexed drawing and the following description set forth in detail one method and one product exemplifying my invention, such disclosed procedure and product constituting, however, but one of various applications of the principle of my invention.

In said annexed drawing:

Fig. l is a more or less diagrammatic view illustrating an apparatus adapted to perform the process embodying my invention; and Fig. 2 is a horizontal sectional view of the pouring crucible incorporated in the apparatus shown in Fig. 1.

Now referring more particularly to the drawing, the apparatus shown therein consists of a cupola I, in which a mixture of graded gray iron scrap and coke is charged, producing the body of molten metal 2 which issues out through the pouring spout 3. The stream of molten metal from the pouring spout 3 next passes into the crucible 4 which has a series of relatively small holes 5 in its bottom wall. The stream from the pouring spout 3 is thus broken up into a multiplicity of relatively fine streams of small cross-sectional area. A resistance coil 6 is assembled around the pouring crucible 4 for the purpose of maintaining the metal therein in molten condition. Immediately below the pouring crucible 4, there is located a turbine or paddle wheel I, driven by the motor 8, and having a series of blades 5 which are adapted to impinge against the series of molten metal streams dropping down from the crucible 4. The blades 9 of the paddle wheel I are constructed of heat resistant material and are inclined at such an angle as to present an impact surface to the molten metal so that the latter is impacted or batted through the air. A water tank Ill is located below the paddle wheel I and at such a distance as to receive the dispersed and batted particles of metal after the latter have become air cooled to a temperature just above the AC1 critical point or just below the solidus temperature.

By means of regulating the speed of the paddle wheel I with relation to the rate of flow of the molten metal from the crucible 4, it is possible to control the range of particle size of the ultimate product. The following example will readily illushate this statement:

Assume that the cupola l is of such capacity as to deliver eight tons per hour and that the pouring crucible 4 is capable of delivering fifty individual streams of molten metal. This would result in the delivery of approximately 5 pounds per minute of molten metal in each of the fifty streams. Assuming also that the paddle wheel 1 has twenty blades rotating at a speed of 1000 R. P. M.; this would mean that there would be 20,000 impacts per minute against each one of the fifty streams of metal, and if each impact is suflicient to produce ten divided or dispersed particles of metal, then 5 lbs. of metal from each of the fifty streams will be broken up into 200,000 particles having an average weight of .011 gram. By reducing the speed of the paddle wheel 1 to one half or 500 R. P. M., the number of impacts to which the 5 pounds of metal would be subjected would then be 10,000. But the force or momenturn of the impact would also be reduced by onehalf so that each unit mass of molten metal impacted or batted by each blade would be broken into approximately only five particles, with the result that each 5 pounds of metal will be dispersed into 50,000 particles of an average weight of approximately .044 gram or four times as heavy as in the case where the paddle wheel is rotated at the rate of 1000 R. P. M.

The foregoing example is not intended to be empirical, but is cited merely by way of illustrating the manner of controlling particle size by means of speed of rotation of the paddle wheel,

or equivalently by means of regulating the rate and force of the impacts against the molten metal streams.

Furthermore, since the metal particle undergo solidification while being air cooled and before contact with the water quench, there is produced a more uniformly spherical shaped particle, probably due to the generally plastic condition of such particles when flying through the air. In addition, this air quench or solidification in air, before the ultimate water quench of the particles, results in a suppression of the undesired dendritic freezing pattern, and of course a predominance of martensitic structure over the cementitic.

The ultimate product will contain the following constituents of the iron-carbon diagram: Martensite or pseudo martensite, in predominance, Lamellar pearlite, Cementite, Ferrite, Graphitic carbon,

This resultant product possesses the physical properties of being sufliciently hard in order to produce the required abrasive action and at the same time sufliciently strong and tough to possess a relatively long life and to withstand the rigorous conditions of usage.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the product and method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

I therefore particularly point out and distinctly claim as my invetntion:

1. A method of making ferrous metal abrasive consisting in the steps of dividing a molten stream of said metal into a plurality of streams of relatively small cross-sectional area, impacting said plurality of streams against moving relatively cool surface to effect the formation of solidified or partly solidified globules of the metal, slowly cooling the globules of said metal resultant from such impact to a temperature just below the solidus temperature, and then rapidly quenching said globules to atmospheric temperature.

2. A method of making ferrous metal abrasive consisting in the steps of dividing a molten stream of said metal into a plurality of streams of relatively small cross-sectional area, impacting said plurality of streams against relatively cool surface immediately followed by movement of the metal over said surface to effect the formation of solidified or partly solidified rotund globules of the metal, air cooling the globules resultant from such impact and movement to a temperature just below the solidus temperature, and then water cooling said globules to atmospheric temperature.

3. A method of making ferrous metal abrasive consisting in the steps of dividing a molten stream of such metal into a plurality of molten streams of relatively small cross-sectional area, subjecting such plurality of streams to impact with a moving relatively cool solid body to effect shattering and formation of said molten streams into globules of the metal, and then collecting and further cooling the hardening globules of said metal resultant from such impact.

4. A method of making ferrous metal abrasive consisting in the steps of subjecting a molten stream of ferrous metal to impact with a moving relatively cool solid surface to effect shattering and formation of said molten stream into globules of the metal, and regulating the size of said globules by varying the speed and force of impact of such solid surface with said molten stream, and collecting and further cooling the resultant globules.

5. A method of making ferrous metal abrasive consisting in the steps of dividing a molten stream of such metal into a plurality of streams of relatively small cross-sectional area, subjecting such plurality of streams to impact with a moving relatively cool solid body and throwing the resultant particles therefrom, then solidifying and cooling the thrown particles of said metal, and regulating the size of said particles by varying the impact speed of such solid body.

6. A method of making ferrous metal abrasive consisting in the steps of impacting a molten stream of said metal against a moving relatively cool solid body and throwing the resultant particles therefrom, slowly cooling the thrown particles of said metal to a temperature just below the solidus temperature, then rapidly quenching said particles to atmospheric temperature, and regulating the size of said particles by varying the speed and force of impact of such solid body.

'7. A method of making ferrous metal abrasive consisting in the steps of impacting a molten stream of said metal against a moving solid body and throwing the resultant particles therefrom, air cooling the thrown particles to a temperature just below the solidus temperature, then water cooling said particles to atmospheric temperature, and regulating the size of said particles by varying the speed and force of impact of such solid body.

8. The method of making ferrous metal abrasive comprising the steps of, impacting a stream of molten metal against a relatively hard cool surface to effect the formation of globules followed by rolling said globules over said surface to effect the formation of solidified or partly solidified rotund globules of the metal, slowly cooling the rotund globules from the melting point to a temperature just above the AC1 critical temperature, and then rapidly cooling said rotund globules to a point approaching atmospheric temperature.

9. The method of making ferrous metal abrasive comprising, impacting a stream of molten metal against a relatively hard cool surface to effect the formation of globules followed by rolling said globules over said surface to effect the formation of solidfled or partly solidified rotund globules of the metal, air cooling the rotund globules to a temperature just below the solidus tem* perature, and thereafter water cooling said rotund globules to a point approaching atmospheric temperature.

10. The method of making ferrous metal abrasive comprising the steps of, impacting a molten stream of said metal against relatively cool moving surfaces whereby said stream is broken up into globules and the globules caused to roll over the surfaces to effect the formation of solidified or partly solidified rotund globules of the metal, slowly cooling the rotund globules thus formed to a temperature just below the solidus temperature, and then rapidly cooling the rotund gldbules by quenching.

11. The method of making ferrous metal abrasive comprising the steps of, impacting a molten stream of said metal against a relatively cool a'dvancing surface to effect the formation of solidified or partly solidified globules of the metal, air cooling the resultant globules to a temperature just below the solidus temperature, and then water cooling the solidified granules.

12. The method of making ferrous metal abrasive comprising the steps of, subjecting the metal while in a fluid form to impact with a moving relatively cool solid surface to effect the formation of metal globules therefrom, and then solidifying and collecting the globules so formed.

WILLIAM H. SHAW. 

